The present invention relates to an emulsifier, and more particularly to an emulsifier useful for preparing aqueous emulsions having a high viscosity.
In emulsion polymerization of unsaturated monomers such as acrylates and vinyl acetate, the use of an emulsifier or protective colloid is essential. Various kinds of non-ionic or anionic surface active agents have hitherto been employed alone or in admixture thereof as emulsifiers, and polyvinyl alcohol or methyl cellulose is employed as protective colloids. The emulsions so obtained are very useful as adhesives, coating materials, fiber and textile processing agents, and the like, but are poor in storage stability, freeze-thaw stability and dilution stability.
In order to improve these defects, it is proposed to employ as emulsifiers or protective colloids, copolymers of vinyl acetate and olefinsulfonic acid salts such as ethylenesulfonic or allylsulfonic acid salts, or the hydrolyzed copolymers thereof. According to the present inventor's study, such copolymers eliminate the above-mentioned defects, but are hard to increase the viscosity of emulsions. In case of coating on porous substrates such as papers and cloths, the low viscosity emulsions are unsuitable because they are absorbed by the substrates, so that desired properties of the coating cannot be sufficiently exhibited. Addition of thickners gives high viscosity emulsions, but is liable to destroy the stability of the emulsions. Accordingly, there is demanded development of an emulsifier enabling to prepare emulsions having a high viscosity.
It is an object of the present invention to provide an emulsifier capable of producing emulsions having a high viscosity as well as excellent storage, freeze-thaw and dilution stabilities.
Another object of the invention is to provide excellent emulsions containing scarcely agglomerates and coarse particles and having an improved flowability in addition to the above-mentioned properties.
These and other objects of the present invention will become apparent from the description hereinafter.